The present invention relates to a process for the preparation of substantially amorphous polymers of alpha-olefins. In particular, the present invention relates to a process for the preparation of substantially amorphous homo- and copolymers of propylene and compositions containing them together with isotactic polypropylene. The present invention relates also to a convenient process for the preparation of indenyl compounds useful for the preparation of metallocenes, which are used in the process for the preparation of substantially amorphous polymers of alpha-olefins.
Products of the propylene homopolymerization can be either crystalline or amorphous. Whereas the polypropylene having isotactic or syndiotactic structure is crystalline, the polypropylene having essentially atactic structure is amorphous.
Amorphous polypropylene finds applications as a component in hot melt adhesives, paper coatings and as a bitumen additive. Generally, it can be obtained as a side product from the preparation of isotactic polypropylene in the presence of heterogeneous Ziegler-Natta type catalysts. This product, however, has moderate molecular weight, broad molecular weight distribution, and contains some residual cristallinity. Moreover, the separation of the fraction of amorphous polypropylene from the remainder product involves an additional step of separation by means of solvents.
For use in a wider range of applications, notably in blends with crystalline polypropylene for PVC replacement, amorphous polypropylene having high molecular weight is required.
More recently, by polymerizing propylene in the presence of particular metallocene catalysts, amorphous polymers of propylene endowed with high molecular weights and a narrow molecular weight distribution have been obtained.
European patent application 604 917, for example, describes amorphous propylene polymers obtained in the presence of bridged bis-fluorenyl metallocenes. The structure of the polymers is substantially atactic, with the syndiotactic dyads being more numerous than the isotactic dyads.
In International application WO 95/00562 it is described a process for producing amorphous poly-alpha-olefins with a monocyclopentadienyl transition metal catalyst system. Both low and high molecular weight polymers can be obtained, with narrow molecular weight distributions. As for the polymers described in EP-A-604,917, also in this case the syndiotactic dyads are more abundant than the isotactic dyads.
These amorphous polymers of propylene find interesting applications in blends with cristalline polyolefins.
In International application WO 96/23838, for instance, there are described blends of high molecular weight amorphous polypropylene with lower molecular weight isotactic polypropylene. The amorphous polypropylene, which are produced by using the same catalyst as in WO95/00562, have more syndiotactic than isotactic dyads.
It would be desirable to make available amorphous alpha-olefin polymers endowed with high molecular weights and narrow molecular weight distributions, which are more miscible with isotactic poly-alpha-olefins. It would also be desirable to provide amorphous alpha-olefin polymers with improved elastomeric properties.
In European patent application EP-A-0 693 506 the preparation of substantially amorphous polymers of propylene in the presence of unbridged bis-indenyl or bis-4,5,6,7-tetrahydroindenyl compounds substituted in the 2-position on the indenyl or tetrahyroindenyl groups is described. In these polymers, the isotactic dyads are more numerous than the syndiotactic dyads. However, when the polymerization is carried out at temperatures of industrial interest, polymers of propylene endowed with low molecular weight are obtained.
In European patent application EP-A-0 584 609 it is described the preparation of polypropylene by means of a metallocene compound, which is used as a mixture of its racemic and meso isomeric form. The obtained polypropylene compositions contain fractions of amorphous and isotactic polypropylene. The miscibility of those fractions can still be improved.
U.S. Pat. No. 5,516,848 and U.S. Pat. No. 5,539,056 relate to the in situ preparation of polypropylene blends comprising high molecular weight amorphous polypropylene with lower molecular weight isotactic polypropylene. It is mentioned that blends containing low molecular weight amorphous polypropylene with high molecular weight isotactic polypropylene have poor elastic recovery properties, due to the stiffness of the isotactic polypropylene.
It has been surprisingly found that it is possible, operating at conditions of industrial interest, to prepare amorphous polymers of alpha-olefins having high molecular weights, narrow molecular weight distribution, with a predominance of isotactic dyads, by carrying out the polymerization reaction in the presence of metallocene catalysts comprising a particular substituted, single-atom-bridged, bis-indenyl compound.
Therefore, the present invention provides a process for the preparation of polymers of alpha-olefins, particularly of propylene, in the presence of a catalyst comprising the product obtainable by contacting:
(A) a metallocene compound in the racemic form of the formula (I): 
xe2x80x83wherein
substituents R1 are hydrogen atoms;
R2 and R3 are, independently from each other, C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals, optionally containing silicon or germanium atoms;
or where R2 and R3 can be joined together to form a 4 to 6 membered ring or a 6 to 20 fused ring system;
R4 and R5, same or different, are hydrogen atoms or xe2x80x94CHR8R9 groups;
R4 and R5 can form a ring having 3 to 8 carbon atoms, which can contain hetero atoms;
the R8 and R9 substituents, same or different, are hydrogen atoms, C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals, which can form a ring having 3 to 8 carbon atoms which can contain hetero atoms;
the R6 and R7 substituents, same or different, are hydrogen, C1-C10-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals, optionally containing silicon or germanium atoms; and optionally two adjacent R6 and R7 substituents can form a ring comprising from 5 to 8 carbon atoms;
M is a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version), X, same or different, is a monoanionic ligand, such as a hydrogen atom, a halogen atom, a R10, OR10, OSO2CF3, OCOR10, SR10, NR10, or PR102 group, wherein the substituents R10 are a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-alkylaryl radical, optionally containing silicon or germanium atoms;
p is an integer from 0 to 3, p being equal to the oxidation state of the metal M minus two; and
(B) an alumoxane and/or a compound capable of forming an alkyl metallocene cation.
In the metallocene of formula (I) the transition metal M is preferably selected from titanium, zirconium and hafnium.
More preferably, the transition metal M is zirconium.
The X substituents are preferably chlorine atoms or methyl groups.
The R6 and R7 substituents are preferably hydrogen atoms.
Non-limiting examples of metallocene compounds of formula (I) suitable for use in the process of the invention are:
methylene-bis(3-isopropyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-isopropyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-isopropyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-isopropyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis[3-(1-methylpropyl)-indenyl]zirconium dichloride and dimethyl;
isopropylidene-bis[3-(1-methylpropyl)-indenyl]zirconium dichloride and dimethyl;
cyclopentylidene-bis[3-(1-methylpropyl)-indenyl]zirconium dichloride and dimethyl;
cyclohexylidene-bis[3-(1-methylpropyl)-indenyl]zirconium dichloride and dimethyl;
methylene-bis[3-(1-methylbutyl)-indenyl]zirconium dichloride and dimethyl;
isopropylidene-bis[3-(1-methylbutyl)-indenyl]zirconium dichloride and dimethyl;
cyclopentylidene-bis[3-(1-methylbutyl)-indenyl]zirconium dichloride and dimethyl;
cyclohexylidene-bis[3-(1-methylbutyl)-indenyl]zirconium dichloride and dimethyl;
methylene-bis[3-(1-phenylethyl)indenyl]zirconium dichloride and dimethyl;
isopropylidene-bis[3-(1-phenylethyl)indenyl]zirconium dichloride and dimethyl;
cyclopentylidene-bis[3-(1-phenylethyl)indenyl]zirconium dichloride and dimethyl;
cyclohexylidene-bis[3-(1-phenylethyl)indenyl]zirconium dichloride and dimethyl;
methylene-bis(3-diphenylmethyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-diphenylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-diphenylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-diphenylmethyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis[3-(1-cyclohexyl)methylindenyl]zirconium dichloride and dimethyl;
isopropylidene-bis[3-(1-cyclohexyl)methylindenyl]zirconium dichloride and dimethyl;
cyclopentylidene-bis[3-(1-cyclohexyl)methylindenyl]zirconium dichloride and dimethyl;
cyclohexylidene-bis[3-(1-cyclohexyl)methylindenyl]zirconium dichloride and dimethyl;
methylene-bis(3-biscyclohexylmethyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-biscyclohexylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-biscyclohexylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-biscyclohexylmethyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-biscyclopentylmethyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-biscyclopentylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-biscyclopentylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-biscyclopentylmethyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-biscyclopropylmethyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-biscyclopropylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-biscyclopropylmethyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-biscyclopropylmethyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-cyclohexyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-cyclohexyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-cyclohexyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-cyclohexyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-cyclopentyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-cyclopentyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-cyclopentyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-cyclopentyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-cyclopropyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-cyclopropyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-cyclopropyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-cyclopropyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-cycloheptyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-cycloheptyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-cycloheptyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-cycloheptyl-indenyl)zirconium dichloride and dimethyl;
methylene-bis(3-norbomyl-indenyl)zirconium dichloride and dimethyl;
isopropylidene-bis(3-norbomyl-indenyl)zirconium dichloride and dimethyl;
cyclopentylidene-bis(3-norbomyl-indenyl)zirconium dichloride and dimethyl;
cyclohexylidene-bis(3-norbomyl-indenyl)zirconium dichloride and dimethyl.
Most preferably the metallocene compounds of formula (I) are methylene-bis(3-isopropyl-indenyl)zirconium dichloride and isopropylidene-bis(3-isopropyl-indenyl)zirconium dichloride.
The preparation of the ligands for the metallocenes of formula (I) can be carried out by different methods. A particularly suitable method for preparing the ligands for the metallocenes of formula (I) wherein R4 and R5 are hydrogen atoms is reported in WO 98/43931. A method for preparing the ligands for the metallocenes of formula (I) wherein at least one of the substituents R4 and R5 is different from hydrogen atoms is described in EP-A 0 722 949 and EP-A 0 722 950. The synthetic routes described therein, however, are rather complicated and involve the use of the toxic and expensive dimethoxyethane (DME). Further, since the above synthesis requires the use of excessive hydroxides, the disposal of not consumed hydroxides involves additional environmental protection measures.
According to a further aspect of the present invention, it is provided a process for the preparation of a compound of formula (II): 
and/or its double bond isomers, wherein R1, R2, R3, R4, R5, R6 and R7 are defined as above; comprising the following steps:
a) contacting a compound of formula (III): 
xe2x80x83and/or its double bound isomer,
wherein R1, R6 and R7 have the meaning as described above, with a base selected from the group consisting of alkali and earth alkali metal hydroxides or alkoxides in the presence of an oxygen containing solvent;
b) treating the obtained corresponding anionic form with a compound of general formula R4R5CO, wherein R4 and R5 have the same meaning as defined above, in order to obtain a compound of the formula (IV): 
xe2x80x83and/or its double bound isomers;
wherein R1, R4, R5, R6 and R7 have the meaning as above mentioned;
c) contacting the compound of formula (IV) with a base, wherein the molar ratio between the base and the compound of formula (IV) is equal to or greater than 2;
d) treating the corresponding di-anionic form of formula (IV) with a compound (V) of formula CHR2R3L, R2 and R3 being as defined above and L is a halogen atom selected from the group 17 of the Periodic Table of the Elements (new IUPAC version), wherein the molar ratio between the compound (V) and the corresponding di-anionic form of formula (IV) is equal to or greater than 2.
The bases, which may be used in step a) are preferably sodium or potassium hydroxide. The molar ratio between said base and the indenyl compound of formula (III) can vary over a wide range. The process of the present invention has the advantage that the base can be used in less than stoichiometric amounts. The molar ratio between said base and said indenyl compound of formula (III) preferably ranges from a catalytic amount to 1. More preferably from 0.01 to 1, and even more preferably from 0.1 to 1.
Preferably, the oxygen containing solvent used in step a) is dimethylsulfoxide (DMSO) or 1-Me-2-pyrrolidinone.
The compound of general formula R4R5CO, which is used in the above step a) for introducing the bridge between two indenyl moieties of general formula (III), can be, for instance, formaldehyde, formaline, acetone, cyclohexanone or cyclopentanone.
The base used in step c) is selected from alkali and earth alkali metal hydroxides, organic lithium compounds and metallic sodium or potassium, preferably the base is buthyllithium.
The contact treatment of compound of general formula (IV) and the base, such as buthyllithium, can be carried out in a solvent such as THF or diethylether.
In the process according to the present invention L is selected from chlorine, bromine, iodine and fluorine, preferably L is bromine. Non-limiting examples of compounds of formula CHR2R3L are, for instance, 2-bromopropane, 2-bromohexane or diphenylbromomethane. The temperature in the reaction medium can vary in dependence of the solvent, the nature and the quantity of the used compounds and is generally in the range of between room temperature and reflux temperature of the solvent used.
The purification of the ligand of formula (II) can be carried out according to general known methods, such as distillation or filtration.
Non-limiting examples of compounds of formula (II) are:
1,1-bis(3-isopropyl-indenyl)methane;
2,2-bis(3-isopropyl-indenyl)propane;
1,1-bis(3-isopropyl-indenyl)cyclopentane;
1,1-bis(3-isopropyl-indenyl)cyclohexane;
1,1-bis[3-(1-methylpropyl)-indenyl]methane;
2,2-bis[3-(1-methylpropyl)-indenyl]propane;
1,1-bis[3-(1-methylpropyl)-indenyl]cyclopentane;
1,1-bis[3-(1-methylpropyl)-indenyl]cyclohexane;
1,1-bis[3-(1-methylbutyl)-indenyl]methane;
2,2-bis[3-(1-methylbutyl)-indenyl]propane;
1,1-bis[3-(1-methylbutyl)-indenyl]cyclopentane;
1,1-bis[3-(1-methylbutyl)-indenyl]cyclohexane;
1,1-bis[3-(1-phenylethyl)indenyl]methane;
2,2-bis[3-(1-phenylethyl)indenyl]propane;
1,1-bis[3-(1-phenylethyl)indenyl]cyclopentane;
1,1-bis[3-(1-phenylethyl)indenyl]cyclohexane;
1,1-bis(3-diphenylmethyl-indenyl)methane;
2,2-bis(3-diphenylmethyl-indenyl)propane;
1,1-bis(3-diphenylmethyl-indenyl)cyclopentane;
1,1-bis(3-diphenylmethyl-indenyl)cyclohexane;
1,1-bis[3-(1-cyclohexyl)methylindenyl]methane;
2,2-bis[3-(1-cyclohexyl)methylindenyl]propane;
1,1-bis[3-(1-cyclohexyl)methylindenyl]cyclopentane;
1,1-bis[3-(1-cyclohexyl)methylindenyl]cyclohexane;
1,1-bis(3-biscyclohexylmethyl-indenyl)methane;
2,2-bis(3-biscyclohexylmethyl-indenyl)propane;
1,1-bis(3-biscyclohexylmethyl-indenyl)cyclopentane;
1,1-bis(3-biscyclohexylmethyl-indenyl)cyclohexane;
1,1-bis(3-biscyclopentylmethyl-indenyl)methane;
2,2-bis(3-biscyclopentylmethyl-indenyl)propane;
1,1-bis(3-biscyclopentylmethyl-indenyl)cyclopentane;
1,1-bis(3-biscyclopentylmethyl-indenyl)cyclohexane;
1,1-bis(3-biscyclopropylmethyl-indenyl)methane;
2,2-bis(3-biscyclopropylmethyl-indenyl)propane;
1,1-bis(3-biscyclopropylmethyl-indenyl)cyclopentane;
1,1-bis(3-biscyclopropylmethyl-indenyl)cyclohexane;
1,1-bis(3-cyclohexyl-indenyl)methane;
2,2-bis(3-cyclohexyl-indenyl)propane;
1,1-bis(3-cyclohexyl-indenyl)cyclopentane;
1,1-bis(3-cyclohexyl-indenyl)cyclohexane;
1,1-bis(3-cyclopentyl-indenyl)methane;
2,2-bis(3-cyclopentyl-indenyl)propane;
1,2-bis(3-cyclopentyl-indenyl)cyclopentane;
1,1-bis(3-cyclopentyl-indenyl)cyclohexane;
1,1-bis(3-cyclopropyl-indenyl)methane;
2,2-bis(3-cyclopropylindenyl)propane;
1,1-bis(3-cyclopropyl-indenyl)cyclopentane;
1,1-bis(3-cyclopropyl-indenyl)cyclohexane;
1,1-bis(3-cycloheptyl-indenyl)methane;
2,2-bis(3-cycloheptyl-indenyl)propane;
1,1-bis(3-cycloheptyl-indenyl)cyclopentane;
1,1-bis(3-cycloheptyl-indenyl)cyclohexane;
1,1-bis(3-norbomyl-indenyl)methane;
2,2-bis(3-norbomyl-indenyl)propane;
1,1-bis(3-norbomyl-indenyl)cyclopentane;
1,1-bis(3-norbomyl-indenyl)cyclohexane.
Most preferably the compound of formula (II) is 2,2-bis(3-isopropyl-indenyl)propane.
The metallocene compounds of formula (I) can be prepared by contacting the corresponding bis-indenyl ligands of formula (II) with a compound capable of forming a delocalized anion on the cyclopentadienyl ring, and with a compound of formula MXp+2, wherein M, X and p are defined as above.
In the case in which at least one substituent X in the metallocene compound of the formula (I) which is to be prepared is other than a halogen, it is necessary to substitute at least one substituent X in the metallocene obtained by at least one substituent X other than a halogen.
The reaction of substituting substituents X by substituents X other than a halogen is carried out using generally applied methods. For example, if the desired substituents X are alkyl groups, the metallocenes can be made to react with alkylmagnesium halides (Grignard reagents) or with alkyllithium compounds.
In the catalyst used in the process according to the invention, both the metallocene compound of the formula (I) and the alumoxane can be present as the product of the reaction with an organometallic aluminium compound of the formula AlR113 or Al2R116, in which the R11 substituents, same or different, are defined as the substituents R8 or are halogen atoms.
The alumoxanes used in the process of the present invention may be obtained by reaction between water and an organometallic compound of aluminium of formula AlR113 or Al2R116, in which the R11 substituents, same or different, are defined as above, with the condition that at least one R11 is different from halogen. The molar ratio between the aluminium and water is in the range of 1:1 and 100:1.
Non-limiting examples of aluminium compounds of the formula AlR113 or Al2R116 are: Al(Me)3, Al(Et)3, AlH(Et)2, Al(iBu)3, AlH(iBu)2, Al(iHex)3, Al(iOct)3, AlH(iOct)2, Al(C6H5)3, Al(CH2C6H5)3, Al(CH2CMe3)3, Al(CH2SiMe3)3, Al(Me)2iBu, Al(Me)2Et, AlMe(Et)2, AlMe(iBu)2, Al(Me)2iBu, Al(Me)2Cl, Al(Et)2Cl, AlEtCl, and Al2(Et)3Cl3, wherein Me=methyl, Et=ethyl, iBu=isobutyl, iHex=isohexyl, iOct=2,4,4-trimethyl-pentyl.
Particularly interesting aluminium compounds are those described in the European application No. 97203332.8 in which the alkyl groups have specific branched patterns. Non-limiting examples of aluminium compounds according to said European application are: tris(2,3,3-trimethyl-butyl)aluminium, tris(2,3-dimethyl-hexyl)aluminium, tris(2,3-dimethyl-butyl)aluminium, tris(2,3-dimethyl-pentyl)aluminium, tris(2,3-dimethyl-heptyl)aluminium, tris(2-methyl-3-ethyl-pentyl)aluminium, tris(2-methyl-3-ethyl-hexyl)aluminium, tris(2-methyl-3-ethyl-heptyl)aluminium, tris(2-methyl-3-propyl-hexyl)aluminium, tris(2-ethyl-3-methyl-butyl)aluminium, tris(2-ethyl-3-methyl-pentyl)aluminium, tris(2,3-diethyl-pentyl)aluminium, tris(2-propyl-3-methyl-butyl)aluminium, tris(2-isopropyl-3-methyl-butyl)aluminium, tris(2-isobutyl-3-methyl-pentyl)aluminium, tris(2,3,3-trimethyl-pentyl)aluminium, tris(2,3,3-trimethyl-hexyl)aluminium, tris(2-ethyl-3,3-dimethyl-butyl)aluminium, tris(2-ethyl-3,3-dimethyl-pentyl)aluminium, tris(2-isopropyl-3,3-dimethyl-butyl)aluminium, tris(2-trimethylsilyl-propyl)aluminium, tris(2-methyl-3-phenyl-butyl)aluminium, tris(2-ethyl-3-phenyl-butyl)aluminium, tris(2,3-dimethyl-3-phenyl-butyl)aluminium, as well as the corresponding compounds wherein one of the hydrocarbyl groups is replaced by an hydrogen atom, and those wherein one or two of the hydrocarbyl groups are replaced by an isobutyl group.
Amongst the above aluminium compounds, trimethylaluminium (TMA), triisobutylaluminium (TIBAL), tris(2,4,4-trimethyl-pentyl)aluminium (TIOA), tris(2,3-dimethylbutyl)aluminum (TDMBA) and tris(2,3,3-trimethylbutyl)aluminum (TTMBA) are preferred.
The alumoxanes used in the catalyst according to the invention are considered to be linear, branched or cyclic compounds containing at least one group of the type: 
wherein the substituents R12 same or different, are C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals, optionally hydrogen atoms, silicon or germanium atoms, or a xe2x80x94Oxe2x80x94Al(R12)2 group and, if appropriate, some substituents R12 can be halogen atoms.
In particular, alumoxanes of the formula: 
can be used in the case of linear compounds, wherein n is 0 or an integer of from 1 to 40 and the substituents R12 are defined as above, or alumoxanes of the formula: 
can be used in the case of cyclic compounds, wherein n is an integer of from 2 to 40 and the R12 substituents are defined as above.
The substituents R12 are preferably ethyl, isobutyl or 2,4,4-trimethyl-pentyl groups.
Examples of alumoxanes suitable for use according to the present invention are methylalumoxane (MAO), isobutylalumoxane (TIBAO), 2,4,4-trimethyl-pentylalumoxane (TIOAO), 2,3-dimethylbutylalumoxane (TDMBAO) and 2,3,3-trimethylbutylalumoxane (TTMBAO).
The catalyst for use in the process according to the invention can suitably be obtained by a process described in the European application No. 97203331.0 comprising the following steps:
(i) contacting the metallocene compound of the formula (I) with part of the described aluminium compound in the absence of water;
(ii) contacting part of the above described aluminium compound with water in the absence of the metallocene compound of the formula (I) and successively:
(iii) contacting the products obtained in steps (i) and (ii).
The part of aluminium compound used in each one of steps (i) and (ii) can consist of the same compound(s) or different compounds.
The molar ratio between the aluminium and the metal of the metallocene compound is in general comprised between 10:1 and 20000:1, and preferably between 100:1 and 5000:1.
Non-limiting examples of compounds able to form an alkylmetallocene cation are compounds of the formula Y+Zxe2x88x92, wherein Y+ is a Brxc3x8nsted acid, able to donate a proton and to react irreversibly with a substituent X of the compound of the formula (I), and Zxe2x88x92 is a compatible anion which does not coordinate and which is able to stabilize the active catalytic species which results from the reaction of the two compounds and which is sufficiently labile to be displaceable by an olefin substrate. Preferably, the anion Zxe2x88x92 consists of one or more boron atoms. More preferably, the anion Zxe2x88x92 is an anion of the formula BAr4(xe2x88x92), wherein the substituents Ar which can be identical or different are aryl radicals such as phenyl. pentafluorophenyl or bis(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl borate is particularly preferred. Moreover, compounds of the formula BAr3 can conveniently be used. Compounds of this type are described, for example, in the published International patent application WO 92/00333.
The catalysts of the present invention can also be used on supports. This is achieved by depositing the metallocene compound (A) or the product of the reaction thereof with the component (B), or the component (B) and then the metallocene compound (A) on supports such as, for example, silica, alunina, magnesium halides, styrene/divinylbenzene copolymers, polyethylene or polypropylene.
A suitable class of supports, which can be used, is constituted by porous organic supports functionalized with groups having active hydrogen atoms. Particularly suitable are those in which the organic support is a partially crosslinked styrene polymer. Supports of this type are described in European application EP-633 272.
Another class of inert supports particularly suitable for use according to the invention is that of the olefin, particularly propylene, porous prepolymers described in International application WO 95/26369.
A further suitable class of inert supports for use according to the invention is that of the porous magnesium halides such as those described in International application WO 95/32995.
The solid compound thus obtained, in combination with the further addition of the alkylaluminium compound either as such or pre-reacted with water if necessary, can be usefully employed in the gas-phase polymerization.
By polymerizing propylene in the presence of the above particular metallocenes it is possible to obtain in high yields, at temperature of industrial interest (i.e. equal to or higher than 40xc2x0 C.), amorphous polypropylene having high molecular weights.
The propylene polymerization process according to the invention can be carried out in the liquid phase in the presence or absence of an inert hydrocarbon solvent, or in the gas phase. The hydrocarbon solvent can either be aromatic such as toluene, or aliphatic such as propane, hexane, heptane, isobutane or cyclohexane.
Although the polymerization temperature and pressure is not critical, the polymerization of propylene is generally carried out at a temperature between 0xc2x0 C. and 250xc2x0 C., particularly between 20xc2x0 C. and 150xc2x0 C., and more particularly between 40xc2x0 C. and 90xc2x0 C. The polymerization pressure is generally comprised between 0.5 and 100 bar.
The lower the polymerization temperature, the higher are the resulting molecular weights of the polymers obtained.
The molecular weight of the polymers can be varied merely by changing the polymerization temperature, the type or the concentration of the catalytic components or by using molecular weight regulators such as hydrogen.
The polymerization yields depend on the purity of the metallocene compound of the catalyst. The metallocene compounds obtained by the process of the invention can therefore be used as such or can be subjected to purification treatments.
The components of the catalyst can be brought into contact each other before the polymerization. The pre-contact concentrations are generally between 1 and 10xe2x88x928 mol/l for the metallocene component (A), while they are generally between 10 and 10xe2x88x928 mol/l for the component (B). The pre-contact is generally effected in the presence of a hydrocarbon solvent and, if appropriate, of small quantities of monomer. In the pre-contact it is also possible to use a non-polymerizable olefin such as isobutene and 2-butene.
The propylene polymers obtainable with the process of the present invention may have a varying content of isotactic sequences. Generally, the percentage of the isotactic triads (mm) is in the range from 10 to 80, preferably from 25 to 50. Therefore, they can be from substantially amorphous to partially crystalline. Their melting enthalpy is generally lower than 70 J/g, preferably lower than 50 J/g, and most preferably lower than 20 J/g. Those polymers with the shortest isotactic sequences show no detectable melting enthalpy.
The structure of the above polymers of propylene is substantially atactic. Nevertheless, it is observed that the isotactic pentads (mmmm) appear to be more numerous than the syndiotactic pentads. Thus, the ratio of the isotactic pentads (mmmm) and the syndiotactic pentads (rrrr) satisfy the relation:
(mmmm)/(rrrr)=1.5, and preferably
(mmmm)/(rrrr)=2.0.
The ratio of the pentads (mmmm) and the pentads (mmmr) satisfy the relation:
(mmmm)/(mmmr)=0.8, and preferably
(mmmm)/(mmmr)=0.9, more preferably
(mmmm)/(mmmr)=1.0.
The tacticity of the polymeric chain, i.e. the distribution of the relative configuration of the tertiary carbons, is determined by 13C-NMR analysis.
The molecular weights of the above said propylene polymers can be quite high. Thus, the intrinsic viscosity can reach values of greater than 0.5 dl/g, even greater than 2 dl/g.
Further, the molecular weights of the propylene polymers are distributed over relatively limited ranges. The molecular weight distribution can be represented by the ratio Mw/Mn which, for the present polymers, is generally lower than 4, preferably lower than 3.5 and, more preferably, lower than 3.
The molecular weight distribution can be varied by using mixtures of different metallocene compounds or by carrying out the polymerization in several stages which differ as to the polymerization temperature and/or the concentrations of the molecular weight regulators.
The structure of the above said propylene polymers appears to be very regioregular. In fact, according to the 13C-NMR, signals relating to sequences (CH2)n wherein n=2 are not detectable. Generally, less than 2% and, preferably, less than 1% of the CH2 groups are contained in sequences (CH2)n wherein n=2.
The polymers of the invention are generally soluble in common solvents, such as, for instance, chloroform, diethylether, hexane, heptane, toluene and xylene.
The polymers of the invention are endowed with good elastoimeric properties as well as with good optical properties, being quite transparent.
The polymers of the invention are transformable into shaped articles by conventional material processing, such as moulding, extrusion, injection etc.
The polymerization reaction according to the invention can be carried out in the presence of ethylene or of a C4-C10 alpha-olefin comonomer. It is thus possible to obtain substantially amorphous propylene copolymers endowed with a good distribution of the comonomer along the polypropylene chain.
Non-limiting examples of alpha-olefins which can be used as comonomers in the copolymers according to the present invention are ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, styrene, 1,5-hexadiene and 1,7-octadiene.
The copolymers according to the present invention are characterized by a homogeneous distribution of the comonomer units within the polymeric chain.
A particular interesting embodiment of the present invention is constituted of a process for preparing copolymers of propylene with ethylene.
The analysis of the distribution of the comonomer units in the copolymers of the invention has been carried out by means of 13C-NMR spectroscopy. The assignments were carried out as described by Randall in Macromol. Chem. Phys.1989, 29, 201. The distribution of triads, in the case of propylene/ethylene, are calculated by the following relationship:
PPP=Txcex2xcex2 EPE=Txcex4xcex4 EPP=Txcex2xcex4 PEP=Sxcex2xcex2 PEE=Sxcex2xcex4 EEE=0.5(Sxcex4xcex4+0.5Sxcex3xcex4 )
wherein PEP, EEP and EEE represent the sequence propylene/ethylene/propylene, ethylene/ethylene/propylene and ethylene/ethylene/ethylene, respectively, in the copolymer. For the NMR nomenclature, see J. Carmen, R. A. Harrington, C. E. Wilkes, Macromolecules, 10, 537 (1977). The values are normalised. The higher the number of isolated ethylene units in the polymeric chain, the more the values of the ratio PEP/(PEP+EEP+EEE) become closer to the unit.
Table 4 refers to propylene/ethylene copolymers obtained with a process according to the present invention.
In particular, in table 4 there are reported the ratios PEP/(PEP+EEP+EEE) as a function of the weight percentage of ethylene in the chain for propylene/ethylene copolymers obtained with a process according to the present invention, in the presence of the above reported metallocene compounds. The amounts of ethylene units being equal, the values of the ratio PEP/(PEP+EEP+EEE) for the copolymers of the invention are always higher than those for the copolymers obtained with metallocenes used in the comparative examples, reflecting the improved distribution of ethylene units in the chain.
In particular, the ratio PEP/(PEP+EEP+EEE) satisfies the following relationship:
PEP/(PEP+EEP+EEE)xe2x89xa70.75
preferably:
PEP/(PEP+EEP+EEE)xe2x89xa70.85
more preferably
PEP/(PEP+EEP+EEE)xe2x89xa70.9.
The copolymers of the present invention have intrinsic viscosity values (I.V.) generally higher than 0.5 dl/g and preferably higher than 0.6 dl/g.
As for the homopolymers, the copolymers of the present invention are generally endowed with a narrow molecular weight distribution. The ratio Mw/Mn for the copolymers of the present invention is generally lower than 4, preferably lower than 3.5 and, more preferably, lower than 3.
The glass transition temperatures (Tg) of the copolymers according to the invention are generally well below 0xc2x0 C., thus allowing the use of articles made thereof to be used at low temperatures.
The propylene polymers of the present invention are particularly suitable to prepare blends with isotactic polymers of alpha-olefins, in particular propylene.
Therefore, it is a further aspect of the present invention a thermoplastic composition comprising:
(A) 1 to 99% by weight of a propylene polymer optionally containing from 0.1 to 20% by moles of units deriving from an olefin of formula CH2xe2x95x90CHR, R being hydrogen, a C2-C20-alkyl or a C6-C12-aryl group, having the following characteristics:
melting enthalpy  less than 70 J/g;
the ratio of the pentads (mmmm)/(rrr)xe2x89xa71.5; and
the ratio of the pentads (mmmm)/(mmmr)xe2x89xa70.8;
(B) 1 to 99% by weight of a propylene polymer, optionally containing from 0.1 to 20% by moles of units deriving from an olefin of formula CH2xe2x95x90CHR, R being hydrogen, a C2-C20-alkyl or a C6-C12-aryl group, having the following characteristics:
melting enthalpy  greater than 70 J/g, and
% of isotactic dyads (m)xe2x88x92% of syndiotactic dyads (r) greater than 0.
In the composition of the present invention the ratio of the quantities by weight of the components (A)/(B) is preferably comprised between 10:90 and 90:10. More preferably, the ratio of the quantities by weight of the components (A)/(B) is comprised between 30:70 and 70:30.
The structure of the above polymers of propylene used as component (A) is substantially atactic. Nevertheless, it is observed that the isotactic pentads (mmmm) appear to be more numerous than the syndiotactic pentads. Thus, the ratio of the isotactic pentads (mmmm) and the syndiotactic pentads (rrrr) satisfy the relation:
(mmmm)/(rrrr)=1.5, and preferably
(mmmm)/(rrrr)=2.0.
The ratio of the pentads (mmmm) and the pentads (mmmr) satisfy the relation:
(mmmm)/(mmmr)=0.8, and preferably
(mmmm)/(mmmr)=0.9, more preferably
(mmmm)/(mmmr)=1.0.
The propylene polymers used as component (A) of the composition according to the present invention may have a varying content of isotactic sequences. Generally, the percentage of the isotactic triads %(mm) is in the range from 10 to 80, preferably from 25 to 50. Therefore, they can be from substantially amorphous to partially crystalline and their melting enthalpy is generally lower than 70 J/g, preferably lower than 50 J/g, and most preferably lower than 20 J/g. Those polymers with the shortest isotactic sequences show no detectable melting enthalpy.
The molecular weights of the above said propylene polymers can be quite high. Thus, the intrinsic viscosity is generally greater than 0.5 dl/g, and can reach values greater than 2 dl/g.
Further, the molecular weights of the propylene polymers used as component (A) of the composition according to the present invention are distributed over relatively limited ranges.
The molecular weight distribution can be represented by the ratio Mw/Mn which, for the present polymers, is generally lower than 4, preferably lower than 3.5 and, more preferably, lower than 3.
The structure of the above said propylene polymers, which is used as component (A) of the composition according to the present invention, appears to be very regioregular. In fact, according to the 13C-NMR, signals relating to sequences (CH2)n wherein n=2 are not detectable. Generally, less than 2% and, preferably, less than 1% of the CH2 groups are contained in sequences (CH2)n wherein n=2.
The melting point of the isotactic polypropylene used as component (B) is generally between 110xc2x0 C. and 160xc2x0 C., and can even reach values above 160xc2x0 C.
The molecular weight of the substantially isotactic polypropylene can be quite high. Thus, the intrinsic viscosity can reach values of greater than 1 dl/g, even greater than 2 dl/g. Preferably, the melting enthalpy of the isotactic polymer of propylene is  greater than 90 J/g.
Examples of isotactic polymers of propylene for use as component (B) are commercial available isotactic polypropylene, which are produced by means of conventional titanium or vanadium based heterogenes Ziegler-Natta-type catalysts. Also can be used metallocene based isotactic polymers having the above described characteristics. Polymers made by means of metallocenes generally have narrow molecular weight distribution Mw/Mn, such as values of lower than 3.
In the above mentioned copolymers, which can be used under (A) and/or (B), the co-monomer can for instance, without any limitation, selected from ethylene, 1-butene, styrene, or cyclohexene.
The melting point of the isotactic propylene copolymers used under (B) is generally between 110xc2x0 C. and 140xc2x0 C. The fraction soluble in xylene at 25xc2x0 C. is generally less than 10%.
The composition of the present invention may contain, as necessary, various additives, reinforcing agents and fillers, such as heat stabilizers, antioxidants, light stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments or dyes, glass fiber, carbon fiber, calcium carbonate, calcium sulfate, barium sulfate, magnesium hydroxide, mica, talc, or clay.
The preparation of the present composition comprising the components (A) and (B) is not critical and can be carried out by a method commonly used in the preparation of conventional polypropylene compositions, wherein melt kneading is conducted with heating, using, for example, a kneader (e.g. kneader, Banbury, rolls) or a single-screw or twin-screw extruder.
The composition of the present invention can be processed in the same manner as conventional polypropylene compositions. They can be extruded, injection moulded, compression moulded, in order to obtain films, fibers, filaments sheets, fabric, wire and cable coatings. For instance, the composition according to the present invention can also be used for the preparation of low-temperature-heat-sealing film.
Article, in particular films and sheets made of the compositions according to the present invention have excellent transparency. A further advantage of the compositions of the present invention is the resistance to blooming. Blooming can be a severe problem in soft polymeric compositions because it causes surface stickiness.
The miscibility of the composition of the components (A) and (B) of the present invention was evaluated by haze measurments (ASTM D1003) and Transmission Electron Micrograph (TEM) microstructures.